The present invention relates to laser diodes. More specifically, the present invention relates to a power supply and control system that regulates and stabilizes the operating conditions of multiple laser diodes.
With the growing importance of fiber optic communication systems and optical memory devices, laser diodes are now one of the most common active devices. In fiber optic communication systems, laser diodes are used as signal transmission components that transmit multi-megabit/second digital data, by being turned ON and OFF at very high data rates to generate the required optical representation of the electrical signal inputs to be conveyed over a fiber optic highway to a repeater or receiver station. Laser diodes are greatly preferred over light emitting diodes in these communications systems because of their ability to operate at extremely high frequencies and transmit data at high rates.
In operating at such high frequencies, however, the light emitted from laser diodes can vary considerably in response to current and power fluctuations, temperature fluctuations, voltage spikes, and aging. Even small variations in these operating parameters can translate to an unacceptable level of noise and impair the laser diode's functionality. Thus, laser diodes require stable external parameters in order to operate properly over long periods of time.
The most important external parameters for proper laser diode functioning are operating current, power and temperature. Consequently, it is of particular importance that the system driving a laser diode include some sort of means that regulates and stabilizes these parameters. This is especially true if the laser diode is undergoing characterization studies, reliability and burn-in production testing, or accelerated life testing before being employed in an optic communication system.
To lessen the effects of these variations, laser diode control systems typically regulate parameters such as the operating current, power, and temperature of the diode. Operating current and power, respectively, are regulated by measuring the current passing through the laser diode output and its operating power level and comparing the measured value to a reference signal. The difference between the reference signal and measured value are used to automatically adjust the operating current or power of the laser diode. Similarly, the laser diode's operating temperature can be regulated by measuring the operating temperature with a temperature sensitive resistor and using a Peltier effect element to heat or cool the diode as necessary.
In controlling the operating parameters it is useful to use a digital processing system such as a personal computer to set the appropriate reference parameters, report on and monitor operating conditions, and adjust diode activity. If the operating parameters of a laser diode become too unstable at any given point, the digital processing system can shut the diode or the entire system off. Prior art control systems based on digital electronics, however, disadvantageously introduce voltage noise that is inherently created by the digital switching processes in the control devices themselves. This voltage noise is passed on to the laser diode and contributes to instable operation which is precisely the fault the digital control system is meant to correct.
It is also practical to drive multiple laser diodes with a single power supply. However, in using a single power supply, extra noise arises from high current required to drive and control the various chips associated with multiple laser diodes. The high current causes interference between parts of the device controlling the individual laser diodes and disrupts diode operation.